1. Field of the Invention
The present invention is related to media control and, more specifically, media control valves used to control the flow of a media into a fluid stream as part of an apparatus for treatment of a surface.
2. Description of the Related Art
A typical media control valve is the pipe side valve shown and described in U.S. Pat. No. 4,322,058, issued to Thompson, et al on Mar. 30, 1982 (the “Thompson Patent”). This valve has been has been widely accepted in applications where the flow of particulate material, such as sand or other abrasive material, from a tank or hopper, is fed into a blast line for propelling the particulate material or media through a nozzle.
As shown in the Thompson Patent, the valve has a unitary plunger which is movable axially with respect to a lateral particulate material inlet between positions closing and opening the inlet. The plunger is moved by rotation on a threaded portion of the plunger through an internally threaded or tapped cap or bonnet opening. The valve body passage through which the plunger is disposed, and the plunger itself, are formed to have abrasion resistant surfaces.
A lateral air pipe nipple sealed to the valve body receives the abrasive material flowing through the valve for use in blasting operations.
Various improvements to the basic media control valve have been proposed. For example, U.S. Pat. No. 5,407,379 (“the '379 patent”) and U.S. Pat. No. 5,401,205 (“the '205 patent”) disclose a media control valve having a media passage between the media control valve and the conduit. The media passage converges into a slot-shaped outlet in the conduit so as to reduce the perimeter of the outlet placed perpendicular to air flow and consequently reduce turbulence as air passes across the outlet. The media control valve disclosed in the '205 and '379 patents is particularly useful in metering and dispensing sodium bicarbonate media. The '045 patent, discussed previously, also discloses a modification of the original media control valve, including the use of multiple seals around a plunger of the valve with an exhaust therebetween to remove any contaminants that breach the seals.
Despite the various improvements in myriad valve designs for a variety of applications, the valve disclosed in the Thompson patent is to this day a widely accepted valve for blasting operations. As desirable as this valve is, there remains room for improvement, especially with respect to wear reduction, as well as repair and maintenance of the valve.
It is desirable to improve on the various prior art designs by incorporating design changes which reduce wear on the valve by the abrasive effects of the media flowing through the valve, particularly during start up. It has been found that the most significant factor in wear is the abrasive action of the media during repeated start and stop cycles. Therefore, modifications in the valve which minimize the effects of abrasion during start/stop cycles will enhance the life of the valve, reduce down time and reduce maintenance and repair costs.